Low Impact Development Ideas and Effects in the Built Environment Joe Sewards UF/IFAS Extension, Volusia county Urban Horticulture agent and Master gardener coordinator
Presentation Outline Predevelopment Fate of Rainfall What is altered when we develop the landscape? What are limitations to our present approach to stormwater? Low Impact Development alternative
Predevelopment Fate of Rainwater Interception rain that never hits the ground lost to evaporation 5-35% Infiltration soil composition (texture) & amount of compaction Depression storage natural depressions throughout the landscape Runoff quantity variable; difference between rainfall rate, infiltration rate & amount of depression storage Runoff rate slow, dependent on slope & roughness of flow path
Reduction of Runoff by Trees
Permeability Post Development Fate of Rainwater (Infiltration) Compaction
Loss of Soil Pore Volume Uncompacted soil Compacted soil 50 % solids 50 % pore space 25% air 25% water Reduced Pore space reduce plant vigor less water storage Slower infiltration rate Faster runoff rate
Soil Structure Impacts Normal soil structure has more microbes, worms, stratification, organic matter and deeper plant roots Post-development (disturbed) soil has far fewer of these critical characteristics
Soil Compaction and Organic Matter Restoration Methods ACTIVITY DECREASE BULK DENSITY (g/cm 3 ) SOURCE Tilling of soil 0.00 to 0.02 (1), (2) Soil loosening 0.05 to 0.15 (3) Selective grading 0.00 (1), (8) Soil amendments 0.17 (2) Compost amendment 0.25 to 0.35 (4) Time 0.20 (5) Reforestation 0.25 to 0.35 (7)
Visualization of Land Use Connection Impervious Native Fertilized Turf Unfertilized Turf Row Crop
Visualization of Land Use Connection Impervious Fertilized Turf Unfertilized Turf Row Crop Native
Low Impact Development? Stormwater and land development strategies at the parcel or subdivision scale that emphasis conservation and use of on-site natural features integrated with engineered, small scale hydrologic controls to more closely mimic pre-development hydrologic conditions. Retain, Detain, Recharge, Filter, Use
Hydrologic/Contaminant Source Control (At the Lot Scale) Control stormwater at the source rain gardens Prevent and treat contamination at the source FFL principles Think micromanagement allow FFL in covenants Reduce imperviousness permeable pavements Minimize disturbance minimize clearing Preserve and recreate natural landscape features utilize existing topography Increase hydrologic disconnects multiple properties Enhance off-line storage cisterns, rain gardens Facilitate detention and infiltration opportunities berms and swales instead of curb and gutter; rain gardens, permeable pavements, larger buffers and other undisturbed areas
Low Impact Development Practices Minimize Impervious Area Green Roofs Rainwater Harvesting Permeable Surfaces Depression storage Bioretention Soil filtration Vegetated Swales Enhance Stormwater Ponds
Rainwater Harvesting Often cleanest water depending on location At the lot scale, typically represents the largest impervious area Depending on storage capacity, significant reduction in source Can be used for irrigation, and slowly released to infiltration, Flush toilets
Depression Storage Rain Garden / Bioretention
Semipermeable Surfaces (Permeable Pavers)
Residential Neighborhood Application (Trench Drain to Median)
LID at the Parcel Scale Infiltration Based - NO Specific Slope Requirement Bio-retention Bio-filters Infiltration Trenches Seepage Pits Pervious Pavement
Putting it together at the developmental scale
Summary Landscape development can result in significant changes in amount and spatial distribution of rainfall interception, infiltration, depression storage and runoff volume and rate. Typical approach to stormwater management is collect, convey, centralize, and control. Conventional centralized management can be very effective, however, there is often a tradeoff between quantity treatment efficiency and quality treatment efficiency.
Summary Low Impact Development attempts to address some of these issues using the following principles: Integrate stormwater management early in site planning activities Use natural hydrologic functions as the integrating framework Focus on prevention rather than mitigation Emphasize simple, nonstructural, low-tech, and low cost methods Manage as close to the source as possible Distribute small-scale practices throughout the landscape Rely on natural features and processes Create a multifunctional landscape
Thank you!!!!! Questions???